It is proposed to investigate the mechanisms of synaptic interaction between cone photoreceptors and horizontal cells. This study will combine the technique of patch clamp recording with primary culture of isolated goldfish retinal cells. Three major issues will be addressed: 1) electrophysiological properties of the postsynaptic channels in horizontal cells, 2) the chemical nature of cone photoreceptor transmitter, and 3) the control by light of transmitter release from cone photoreceptors. In the first stage of the proposed research, the ionic selectivity and kinetic parameters of L-glutamate and L-aspartate activated channels in horizontal cells will be studied. In the second stage, an excised patch of horizontal cell membrane will be used to study channels activated by photoreceptor-released transmitter. An unequivocal identification of the transmitter will be made by comparing the kinetics of the channels activated by natural transmitter to the kinetics observed when known substances are applied to the patch. Using excised patches from horizontal cells as a detector, the control and time course of photoreceptor-released transmitter will be studied.